Method of normalizing steel



Patented Dec. 17, 1935 LIETHOD OF NORMALIZING STEEL William C.Chancellor, Elyria, Ohio, assignor to National Tube Company, acorporation of New Jersey No Drawing. Application April 18, 1933,

, Serial No. 666,732

4 Claims.

This invention relates to methods of treating steel and moreparticularly to methods of treating steel products comprised of steel ofthe'socalled non-austenitic type to produce a desired and beneficialcrystal structure therein.

Heretofore in the art it has been customary when it is desired to obtaina so-called grain refinement in steel products comprised of steel of theso-called non-austenitic type to heat the steel to temperaturesapproximating but above the critical temperature for a time intervalsufficient to obtain entire conversion of the steel to its gamma oraustenitic form and then to cool the steel to a temperature below thelower critical temperature to transform the I austenite to its ferriticor alpha form.

It is known that the toughness of non-austenitic steels depends largelyon the amount and arrangement of excess ferrite which. together withsome form of pear1ite'or sorbite constitutes the structural compositionof such steels. I have found that, in the art of normalizing asheretofore practiced, this excess ferrite is often incompletelydeveloped during the changes which take place when the steel 'coolsthrough the critical temperature range, and the deficiency in excessferrite causes a lowering of resistance to impact and a decrease. intoughness.

One of the objects of the present invention is to provide a method oftreating steel which will operate to produce a uniform grain structureindependently of the prior history of the steel.

Another object of the present invention is to produce a structurecontaining a maximum proportion of excess ferrite consistent with thechemical composition of the steel.

A further object of the present invention is to provide. an improvedmethod of normalizing steel.

Still another object of the present invention is to provide an improvedmethod for normalizing" the grain structure of fabricated steel productssuch as sheet, rods, bars, rails and the like.

Other objects and advantages will become apparent as the invention ismore fully disclosed.

In accordance with the objects and advantages I have discovered that thenon-uniformity of the grain or crystal structure of steel normalized bythe method heretofore proposed in the art can be substantiallyeliminated'by subjecting the steel while cooling through the criticalrange to what may be Broadly defined as an internal agitation ordisturbance. Preferably this internal agitation or disturbance is notaccompanied by any material or permanent alteration of the externalsize,

Shape or configuration of the steel article, but in some instances somepermanent reduction in area may accompany the internal agitation ordisturbance.

The'preferred type of internal agitation or dis- 5 turbance is obtainedby flexing the steel through the application thereto of alternatetensile and compressive stresses. Preferably also the application ofthese alternate tensile and compressive strains should be madetransverse to and pro- 0 gressively along the longitudinal axis of thesteel product.

By. reason of this internal agitation or disturbance the non-uniformsized austenite crystals formed at the temperature of heat-treating are15 broken up during transformation and caused to recrystallize intosmaller grains than tend to develop when agitation is absent. By furtherreason of this internal agitation the separation of excess ferrite fromthe pearlitic constituents 20 is rendered more complete and tends toform a network of ferrite around the pearlitic grains; which type ofstructure is best suited to withstand impacts and sudden deformationwithout failure. As the customary rate of cooling through the 25critical temperature range is relatively slow, the application of theinternal agitation or disturbance should be terminated as soon aspractical after the steel has passed through the transformationtemperature and before cold working eflects 30 incident to such internalagitation and disturbance developto a deleterious or undesired extent.

As a specific embodiment of the practice of the present invention ofwork-normalizing steel the method as applied to steel sheets will bedescribed. 35

The steel sheets are first heated to a temperature approximating butabove the upper critical temperature which temperature will varysomewhat depending upon the specific steel composition and carboncontent. Then the sheet is al- 40 lowed to cool slowly in still air downto a temperature withinthe critical range but above the transformationtemperature and passed lengthwise through staggered rolls positioned tobend the present invention as it is independent of the specificapparatus employed. One skilled in the art of rolling sheet can readilyadapt apparatus to practice the present invention.

In the application of the present invention to elongated articles suchas rails, bars, rods and the like substantially the same'practice asdescribed with respect to sheet may be employed.

In the adaptation of the present invention to tubular articles such asseamless tubing the tinished rolled tube is heated to its normalizingtemperature, which is above the upper critical temperature, and thenwhile the tube is cooling from that temperature through the criticalrange is run through the reeling, sizing and cross-rolling machinesheretofore employed in the art. The action of these machines results atfirst in a distortion of the circular section of the tube to an ovalshape, and then reshapes the same to a circular section of substantiallythe same size as the original tube, thereby introducing within the metalstructure the desired internal agitation or disturbance. In someinstances there is a slight reduction in area accompanying the internalagitation or disturbance which is not-deleterious due to the temperatureat which it is applied.

The advantages obtained by the practice of the present invention arereflected in the physical properties of the steel product resultingtherefrom. I have found that as a result of the better grain refinementobtained, the steel product is found to be tougher, and to show greaterresistance to impact and exhibits greater freedom from f brittleness ascompared to steel products heretofore produced by the prior artnormalizing method. By the practice of the present invention it is notnecessary to closely control the temperature to which the steel isheated, nor is it necestsary to vary the temperature of heating with 40.

slight variations in chemical composition of the .steel as is requiredin the prior art normalizing method. These advantages all serve. tosimplify and to improve the art of normalizing steel.

It is apparent from the above description of the present invention thatthe broad inventive idea of the present'invention is capable ofextensive modification and adaptation in the application oi the sameand. all such modifications and adaptations are anticipated as may fallwithin the scope of the following claims.

What I claim is:

1. The method of treating steel which comprises heating the steel to atemperature slightly 1 above the critical temperature range, cooling thesteel to a temperature below the critical range, and subjecting thesteel during cooling through the critical range and while aboveitstransforma-,.

tion temperature to alternate tensile and compressive stresses effectinga slight reduction in area. Y I

2. The method of treating steel which comprises heating the steel to atemperature slightly above the critical temperature range, cooling thesteel to a temperature below the critical range,

and subjecting the steel during cooling through the critical range andwhile above its transformation temperature to alternate tensile andcom--.

' prises heating the steel to a temperature slightly I above thecritical temperature range, cooling the steel to a temperature below thecritical range, and subjecting the steel during cooling through thecritical range and while above its transformation temperature tomechanical deformation, said deformation including the application ofalternate tensile and compressive stresses applied transversely andprogressively along the length of the steel.

WILLIAM C. CHANCELLOR.

